FOCUS
WAVEFRONT control
surfaces with spatially tailored optical, wetting or tribological properties. Dynamic polarization shaping also provides another promising degree of freedom. By spatially and temporally tailoring the polarization state, including through sequences of ultrashort pulses with controlled polarization, laser – matter interaction can be driven towards specific nanoscale organizations. Recent work on polarization-tailored double-pulse irradiation, for instance, has demonstrated new routes for controlling laser-induced nanostructures, further extending the possibilities offered by structured light beyond intensity shaping alone [ 2 ].
These concepts are already moving from laboratory demonstrations towards demanding industrial applications. In ophthalmic surgery, for example, spatial beam shaping and parallel delivery of femtosecond pulses can accelerate photodisruption while maintaining the precision required for transparent biological tissues. Such an approach illustrates an important evolution of ultrafast processing: beam shaping can increase throughput without simply increasing the local deposited energy.
Perhaps one of the most striking recent developments concerns 3D additive manufacturing( see Figure 2 d-e). Photopolymerization traditionally builds an object sequentially, voxel by voxel or layer by layer. Tomographic volumetric additive manufacturing instead projects a sequence of two-dimensional patterns from different angles into a rotating photosensitive resin, accumulating the optical dose only where the desired three-dimensional object must polymerize. Recent work by Álvarez- Castaño et al. introduced holographic phase encoding into this process [ 5 ].
This result illustrates particularly well the paradigm introduced by wavefront shaping: rather than moving a single laser spot faster, the complete three-dimensional distribution of light can become part of the manufacturing process itself. From massively parallel ablation to non-diffracting cutting, polarization-controlled nanostructuring and volumetric additive manufacturing, structured light provides a route towards faster processing while simultaneously extending the range of structures that can be fabricated.
CURRENT CHALLENGES & PERSPECTIVES Despite impressive demonstrations, several challenges still limit the widespread use of dynamic beam shaping in industrial ultrafast laser processing. As discussed previously, real modulators suffer from finite
Figure 2. Applications of spatial beam shaping to ultrafast laser processing.( a) Parallel surface processing using multiple simultaneously generated laser spots.( b) Multipoint femtosecond laser processing for ophthalmic surgery( Keranova FemtoMatrix).( c) Bessel-beam processing, exploiting an extended depth of focus and self-healing properties for high-aspect-ratio cutting.( d) Holographic tomographic volumetric additive manufacturing, illustrating the fabrication of a complete 3D object by spatially shaped light( e) Spatial beam shaping for photopolymerization of complex microstructures.( a) Adapted with permission from W. Perrie,( c) Adapted from Bhuyan, M. K., F. Courvoisier, P. A. Lacourt, et al. with the permission of AIP Publishing,( d) Adapted from [ 5 ] under CC BY 4.0,( e) Adapted from Yang, Liang, Jiawen Li, Yanlei Hu, et al. Optics Communications 331, 82( 2014), with permission from Elsevier.
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